cellular microorganisms

• Prokaryotes are the smallest and structurally simplest true-living organisms, lacking a nucleus and other membrane-bound organelles
• Prokaryotes include all members of Domains Archaea and Bacteria
• Bacteria (Domain Bacteria) feed primarily on dead organic material
• Some bacteria are photosynthetic, like cyanobacteria, which have chlorophyll and a bluish pigment called phycocyanin
• Cocci are spherical organisms that can be round, oval, elongated, or flattened on one side
• Bacilli are rod-shaped organisms, with some appearing ovoid (coccobacilli) or curved (vibrios)
• Spirals have one or more twists and can be helical like a corkscrew; spirochetes are helical and flexible
• Arrangement of flagella on bacterial cells:

  • Monotrichous: single polar flagellum
  • Amphitrichous: single flagellum at each end of the cell
  • Lophotrichous: two or more flagella at one or both poles
  • Peritrichous: flagella distributed over the entire cell
• Archaea are prokaryotes that lack peptidoglycan in their cell walls and live in extreme conditions
• Archaea are among the simplest, most primitive forms of life, lacking a nucleus and other membrane-bound organelles
• Some groups of Archaea, known as extremophiles, live in extreme environments like hot sulfur springs, saline lakes, and highly acidic or alkaline conditions
• Not all prokaryotic autotrophs derive energy from photosynthesis; some, called chemosynthetic bacteria, use chemical compounds like hydrogen sulfide to convert CO2 into organic matter
• In single-celled organisms, substances can easily enter the cell due to a short distance, while in multicellular organisms, the distance is larger because of a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen due to their higher surface area to volume ratio
• Eukaryotes (Domain Eukarya) possess a nucleus enclosed by a membrane that encloses the DNA in each of their cells
• All prokaryotes (domains Archaea and Bacteria) are unicellular, while eukaryotes include both unicellular and multicellular organisms
• Kingdom Protista (the Protists) can be autotrophic or heterotrophic, unicellular or multicellular, but all are eukaryotic (Domain Eukarya)
• Algae are a diverse group of protists that perform photosynthesis using photosynthetic pigments, distinct from plants, lacking cell walls, specialized tissues, flowers, leaves, stems, and roots
• Diatoms are unicellular algae with cells enclosed by silica cell walls, important primary producers in temperate and polar regions, accounting for a large share of organic carbon produced on Earth
• Dinoflagellates are planktonic, unicellular protists with two flagella, important primary producers, some species release toxic substances causing harmful "red tides" and are bioluminescent
• Fungi are eukaryotic organisms belonging to the Kingdom Fungi, all are heterotrophic, can be unicellular or multicellular, and are important decomposers in the marine environment
• Fungi have a true nucleus, a wall of chitin, can be uni- or multicellular, include molds, mushrooms, yeasts, slime molds, and reproduce through budding, hyphal extension, or spore formation
• Fungi are classified into five phyla based on their mode of sexual reproduction, with significance in medical, veterinary, industrial, and agricultural fields
• Some bacteria have flagella or pili on their surface, allowing them to move or attach to other surfaces.
• The bacterial cell wall is composed of peptidoglycan, which provides structural support to the cell.
• Bacteria are prokaryotic cells that lack membrane-bound organelles.